Automatic wide range electrical wave generator of high stability



Sept. 18, 1951 H. A. ROBINSON AUTOMATIC WIDE RANGE ELECTRICAL-WAVEGENERATOR OF HIGH STABILITY 2 Sheets--fSl'leerl l Filed March 15, 1948ATTORNEY Sept- 18, 1951 H, A. ROBINSON AUTOMATIC WIDE RANGE ELECTRICALWAVE GENERATOR OF HIGH STABILITY Filed March 15, 1948 HARR A. ROBI ON BYl I ATTQRNEY lesser number of crystals, say for example, one and meansfor developing and selecting harmonics of the stabilized oscillationsand feeding them to the mixer I0. The frequency spacing between theharmonics or between adjacent crystals of the group as shown in Fig. 1is small enough to be within the tuning-range of the discriminatorsreferred to hereinafter.

The oscillatory energies from source 8 and from source I2 are mixed inconverter I0 and the difference frequency selected and fed to twofrequency discriminators I8 and 20. One of these discriminators, forexample I8, has a wide characteristic as shown by the curve labeled W inFig. 3. In other words, this discriminator characteristic is representedby a curve of slow or gradual slope. The other discriminator 20 issharp, having a characteristic as illustrated by the curve S, Fig. 3,whose slope rises at an accelerated rate with respect to the slope ofthe Wide band discriminator. A single discriminator with an appropriatecharacteristic may replace the wide and sharp discriminators shown here.These discriminators are tunable by a control means DC shownschematically, and the range of tuning covers the interval betweenadjacent crystals of the reference source I2. This tuning range covers aband 100 kc. wide, extending from 400 to 500 kc. in the example beinggiven.` This tunable discriminator is a feature of my invention, as willappear hereinafter. The control DC for these discriminators is manualand is one of the two manual controls used for selecting any one of thelarge number of frequencies made available. The discriminators may beconventional and may be of the type disclosed in Seeley U. S. Patent#2,121,103 or in Conrad U. S. Patent #2,057,640 or modificationsthereof. In Fig. 2, I illustrate a preferred form of discriminator whichis disclosed and claimed in detail in my U. S. application Serial No.101,079, filed June 24, 1949.

-Each discriminator output includes a direct current component, theabsolute magnitude of which depends on the frequency of the differencefrequency fed from mixer I to the discriminators. These outputs areadditively combined (in series or in parallel) in units 22 and 24 andfed to a reactance tube RT and to a tuning motor control TMR. Thereactance tube may be conyentional being, for example, substantially asdescribed in Crosby Patent #2,279,659 dated April 14, 1942 and isincluded as a reactance in the master oscillation generator 8 in allpositions of tuning thereof. The tuning motor control TMR controls thedirection of rotation of tuning motor TM which tunes the oscillator 8and related equipment. The tuning motor may comprise two field windingsand a rotorwhich rotates in one direction when one eld winding isexcited and in the other direction when the other eld winding isexcited. Then the potential at |20 controls switching means for excitingone or the other winding depending on the absolute magnitude of thepotential at |20. This switching means may comprise a pair of tubes withoutput relays operating in opposed sense to control the position of anarmature which in turn completes the fleld winding circuits. Accurate orexact tuning may be said to be carried out by the reactance tube RT andrough tuning is carried out by the motor TM. Moreover, the latterprovides the feature of automatic tuning.

Returning now to the discriminators I8 and 20, the same are tunable overa frequency range sufcient to cover the frequency intervals betweenadjacent crystals that may be switched into th oscillator circuit at I2or between adjacent harmonics when a single crystal (or smaller group)is employed. This is an important feature of my invention, since by thismeans I am able to generate wave energy of stable frequency and toreadily change the frequency of the wave energy to any desired frequencythrough a Wide range of frequencies and to do so with a small number ofcrystals.

In describing the operation, it will be assumed that the oscillators,mixers, automatic frequency system and so forth are in operation and Iam going to change the frequency of operation. The appropriate crystal(determined by the desired frequency) is selected at I2 by moving theswitch S to include the same in the oscillation generating circuit. Thediscriminator tuning is also adjusted to be appropriate for thedifference frequency resulting from mixing the selected crystal output(or equivalent harmonic) with output from the master oscillator 8. Thedials or scales on switch S of I2 together with the discriminator tuningcontrol DC make this selection of the desired frequency direct reading,being calibrated to denote the master oscillator frequency. To assurethat the master oscillator will be near the selected frequency a tuningadjustment of 8 is usually necessary to bring the master oscillator to afrequency such that the difference frequency out of the mixer I0 will bewithin the frequency range of the discriminator response characteristic.This tuning adjustment may be either manual or automatic. The automatictuning is s accomplished by the tuning motor TM. In this typicalarrangement, the motor drives the master oscillator 8 and associatedtuning controls to a reference position (low frequency end of theoscillator tuning range) during the period while the frequency selectioncontrols S and DC are being set. Upon completion of the setting of thesecontrols, the tuning motor TM tunes the master oscillator 8 (andassociated equipment) through the frequency bandscanning the band-untilthe difference frequency passes through the range of response of thediscriminators I8 and 20, these discriminators then taking over thefinal control of the tuning. During this operation, the broaddiscriminator charac- .I teristic is effective first to operate throughthe reactance tube RT and motor TM to tune the master oscillator 8toward the proper frequency and when the difference frequency out of I 0is brought within the range of the sharp discriminator 20, the tuningaction is accentuated to bring master oscillator 8 to the desiredfrequency setting. A

When the master oscillator 8 serves as the heterodyning oscillator inthe receiver and/or an exciter for a transmitter, the arrangement may besomewhat like that disclosed in my U. S. Patent #2,419,593, dated April29, 1947. The additional apparatus necessary to put said oscillations touse may be as indicated in Fig. 1. Then the master oscillator 8 suppliesoutput to the receiver converter 30. Converter 30, R. F. amplifier 34,I. F. amplifier 36 and .detector-audio amplifier 40 may be conventionalelements of a normal superheterodyne receiver such as are Well known inthe art. If the frequency range is to be extended as in the usualmulti-band receiver-transmitter, a frequency multiplier 32 may beinterposed between the master oscillator 8 and the converter y30. Inthis typical example, the receiver has six bands a selected one of whichmay be switched in "iby control .i0 which raflso iactuates .switch-"2S,There lare induc'tors and Vtrimmer condensers :flor .each `:band in :thefR. iF. vamplifier .stages 14, 'aref -quency `multiplier 3,2 and `:input.circuits :of the converter 30. The .control i0 when .switching bands,also determines .the required frequency multiplier (:N=1, 2, 3, A4, 6)Yand mayswitehaselective I. circuits in AA36 `for several .band widthsas fdesired when operating at ihigher frequencies. To simplify thedescription, `,the .tuning sequence in .one 'band .only .thas beendiscussed. The =radio frequency .amplifier :3.4 `and frequencymultiplier .82 are .tunable .over each frequency zband logreI suitable.tuning means :ganged with `the master oscillator 8. As vpreviouslydescribed, these. ganged circuits may be.automatically-tunedibythermotor TM. The intermediate Ifrequency4.amplifier 36 is ixed -in tuning ibut includes a .s electixzity'zorhand width control which :is .actuated '.by the oo ntroli.

If the `apparatus is :to include `a transmitter .es well asa-receiverandlthesameis to operatelgonfthe same frequency .used by thereceiver, the output of the :frequency multiplier `32 .is alsocoupiledzto a 'transmitter mixer .6:0 which :is excitedby an termediatefrequency `oscillator A:t2 lof stable frequency such as ra .crystal.controlled oscillator. Since Lthe oscillator 02 operates :at .thefrequency of vthe intermediate "frequency .amplifier .3.6, ,all that isnecessary :is to select the desired sum `:or difference I:frequency fromfthe-mixer s60 ito .derive the transmitter oscillatory energy at theire.- quency being received. 'In the .embodiment .de-

scribed, :the vradio .frequency amplifier 34 is used as a .pre-.amplierfor the .transmitter exciter 4in whichcase the switch .S"' is moved tto'the number two position `as is the switch 'S' so that'the foscillatory`energy o f the `.desired frequency, selectedeas described 'hereinbeflorais zamplified :ait

3,4 :and =fed to .intermediate power Iampliiier stages :in -atransmitter for exciting the same. The arrangement iin this respect .isy.quite Vlilref'the arrangement disclosed Iin my `U. iS. Patent#2,419,593, dated April 29, .119A7.

In Eig. 2, I have .shown .one form .of Lthefdis.- criminators which .may'be used .-.at 'I8 .andi-0.0i Eig. t1. This figure .-also `'includestube 190, :which is in sthe mixerstage .I.0. This 4tube .90 has `its rstland third ygrids lcoupled respectively .to .the sources e8 and :I:=2.`These vgrids are ybiased in a conventional :manner :by vbeing.connected .to ground eby resistors to completebiasing circuits throughthe cathode resistor vand condenser .un'it '9:I to the cathode. `Theanode of lthis tube iis coupled 'by coupling f condenser 93 totheeontrol grid of Sa .tube .1I 00, :the cathode of which i-is-.inseries with ithe primary Winding fof an :untuned coupling transformer T`feeding corresponding electrodes of dioderectiers DI and D2. `The anodeof this tubefBIl .isfalsocoupledibv condenser |03 to the control grid ofan amplier stage tube I IIl. Thiscontrolgridisebiased in a conventionalmanner by a `grid resistor connecting the grid to ground and a'cathoderesistor and condenser A.unit connecting .the cathode `to ground. :'.The

anode of tube IIl0 is coupledctoa tuned circuit comprising capacitor C.and nduetor .Lfand the potential 'developed acrossthis tuned circuit isfed bycondenser CI to the mid point of thesesondary .Windingofthefbroa'd.untunedcoupling responsive Yand fthe `difference frequencydoltage developed shirts-in phase asfthefrequeneychanges near 1theresonance :of LC. "This tfrequencyzde, pendent voltage is ishifted @inphase fa-,fxedamolml by @I "RI and :fed in .parallel relation .to.zthefdiode DI and lD2 .electrodes so thatlthe voltageson the diodes arethe fresultants .of .these last voltages and .the .pushfspull .voltage.applied yat "-I. *Then thedifferential detector .output tvoltageVDIMaries as Mthe I. fF. frequency :changes `in generallas saidfSeeleypatent.

' v"The vdamping .of the circuit 'LC .determines :the Width .of .the.discriminator characteristic land since the .tubes and circuit:described are .'desiginated-:asbeing :in the sharp discriminator 1.20,L@ is fle'ft iundamped. The anode .of ltube .9.0 Vis also coupled "tothe .Wide .discriminator I8 .and this discriminatorie similar in ynearlyall :respects :to .the discriminator 2.0. 'fIo .the `elements of -thisdiscriminator :20, I 'have applied fnumerals .conlresponding to thenumerals -orletters used .in de- Scribing the :elements in thediscriminator 20, .but have :primed .said numerals or letters. "In rthe`discr-im'inator It, a damping resistor -DR v'is connected in shuntto-the Etuned circuit LC and ithe vimpedance of .this :resistancedetermines the damping of :the circuit and the effective width of the.discriminator. The. discriminator `2 0 .might then have a4characteristic es .illustrated :at S in Eig. .-3 lwhile thediscriminator 4I8 ihas a charac.- teri'stic as illustrated -atiW in Fig.3. AThe '.detectors in the discriminator 20 fhave --their cathodes.connected .by resistors 1HE and H9. lThe resistors are shunted byVcapacitors 5If|2 and iIfIl3 .which .bypass` any intermediate frequencyenergy reaching ithedetectors andaalso vfixthetimelof-fthe circuits so:that the potentials developed thereacross follow .-onlyfslow changes in`the :frequency of the intermediate -frequencyout vor .the mixer f1.0. Apoint von 'resistor H9 .isgroundedsortha't the voltage 'VDI atthenngrounded. end .varies Vplus to minus and vice versa as thevfrequency shifts throughthe crossover point of thediscriminator larly.connected Aand :operated ilhe .potential dropsfacross thefresistors1.Ii.I'5, .H3 `and IlI-5, Ille may be fed .in .series or -in parallel toterminal :L20 @from which 4they Vare Isupplied `to the greactance tube.and f-to -a control `tube Pin the Vmotor Ltuningcontrol unit Tuningtakes place las long as a potential of material Amagnitude Yissdevelopedat Opoint I 210, and this potential sofa sign -totunethe oscillator -8in a direction to -reducethe potential at I 20 to zero.

By tuning thefcircuit LC, -I -cause-thecrossover points ofdiscriminators IBand 20-to vary through the desired Ktuning range. `Inthis application, the tuningrange 4,00 to '50o-ko, so vthat on selectionof any one of the frequencies (spaced Yevery 100 kc.) Aloy selection ofa crystal at I2, setting o f the ,control dial -DC Iwill itune thediscriminators-'I*8'and`20. Only whenthe difference frequency `out ofmixer I0 vfalls at `the cross- -over point, `is 'the potential at |20zero, ia-ridtjhe automatic tuning operation gis complete. Then theoscillator -8 will be generating oscillations of the desired k'frequencyselected and saidA frequency --may be read directly off the dials for 'Sandthe eontrorDC; Assume for example, energyjistobe generated atoscillation `genera-tor Ifito be-used -in the -receiver tuned --to a-Wave of 2 f11vfmegacycles. 'Thewswitch YSand-control15l are operated A`together f and setto .the l001-ke. marking nearest rthe desiredl'-irequency:(-'2;\1mc.- in this example) 'Seselects ha Icrystal--operating at =-3i3 mc v`'When thec'ontro'l wasv operated, Vthe 'motortuner'rst tuned the circuits in 34 and in 8 to the low frequencyreference end of the band. The frequency of I. F. amplifier 36 isassumed to be 0.7 megacycle So that to get this I. F. the oscillator 8must operate at 2.81 mc. when the R. F. is at 2.11 mc. as assumed above.The dial DC is then adjusted to read 10 kc. which tunes thediscriminators I8 and so the crossover points of their characteristicsare at 490 kc. When the setting of this control is complete, the tuningof the master,l oscillator 8 is .adjusted manually or automatically aspreviously described. As the oscillator 8 approaches 2.81 mc. thedifference frequency out of mixer I0 sweeps into the responsecharacteristics of the discriminators I8 and 20 and potential isdeveloped at |20 to operate through the motor TM and reactance tube RTto tune the master oscillator 8 to bring the potential at |20 to zeroand then the oscillator 8 Will be operating at the frequency set bycontrol 50 (S) and by DC. This automatic tuning may be extended to theband switching elements connected to dial 50, in which case the control50 and controls operated by the motor TM are ganged as indicated bydotted line GC. It will be obvious that even if the discriminatorresponse is inaccurate, say le of one percent of the I. F. (it can bemore accurate) the error is a very small percentage of the masteroscillator frequency. Thus, for each crystal setting at S, I provideoutput of substantially constant frequency at any frequency in a 100 kc.segment and by selection of another crystal any frequency in another 100ko. segment, etc.

The useful frequency range of the controlled master oscillator may beextended by employing a frequency multiplier (harmonic generator) at 32before the excitation is injected into the converter or transmittermixer G0. The order of harmonic developed in 32 is determined by theband switch operated through control 50.

What is claimed is:

l. In apparatus for generating oscillatory energy of substantiallystable frequency, the frequency of which may be changed at willcontinuously through a wide range of frequencies, an oscillationgenerator of controllable frequency, an oscillation source ofsubstantially fixed frequency, a frequency converter directly coupled toboth the oscillation generator and to said source to be excited byoscillations therefrom, narrow and wide band frequency discriminators,both turnable Aat will through a frequency range starting at a frequencyof the order of a side band frequency, coupled to said frequencyconverter to both be excited by side band energy therefrom,

and a control circuit coupling said discriminators to said oscillationgenerator to control the frequency of operation thereof.

2. In apparatus for generating osculatory energy of stable frequency,the frequency of which may be changed at will through a wide range, anoscillation generator of controllable frequency, a source ofoscillations operative at a selected one of a plurality of substantiallyxed frequencies separated each frequency from the other by substantiallyequal frequency intervals, a frequency converter directly coupled tosaid oscillation generator and to said source, frequency controlapparatus for said oscillation generator, a frequency discriminatorapparatus tunable at will through a frequency range substantially equalto said frequency intervals and including the frequency of the lowersideband produced in said converter, means coupling said discriminatorap- Number paratus, to said frequency converter, and a cou-I plingbetween said frequency discriminator apparatus and said frequencycontrol apparatus, the means used to select the desired one of theplurality of xed frequencies having suitable indicia thereon and themeans used to tune the tunable discriminator having suitable indiciathereon, whereby the frequency to which the os" cillation generator iscontrolled may be accurately determined from such indicia.

3. In apparatus for generating oscillatory energy of sta-ble frequency,the frequency of which may be changed at will through a Wide range, anoscillation generator of controllable frequency, a source ofoscillations operative at a selected one of a plurality of substantiallyfixed frequencies separated each frequency from the other bysubstantially equal frequency intervals, a frequency converter directlycoupled to said oscillation generator and to said source, frequencycontrol apparatus for said oscillation generator, a frequencydiscriminator apparatus tunable at will through a frequency rangesubstantially equal to said frequency intervals and including thefrequency of the lower sideband produced in said converter, saiddiscriminator apparatus including Iboth wide and narrow band frequencydiscriminator circuits, means coupling said discriminator apparatus tosaid frequency converter, and a coupling between said frequencydiscriminator apparatus and said frequency control apparatus.

4. In apparatus for generating oscillatory energy of stable frequency,the frequency of which may be changed at will through a wide range, anoscillation generator of controllable frequency, a source ofoscillations operative at a selected one of a plurality of substantiallyfixed frequencies separated each frequency from the other bysubstantially equal frequency intervals, a frequency converter directlycoupled to said oscillation generator and to said source, frequencycontrol apparatus for said oscillation generator, a frequencydiscriminator apparatus tunable at will through a frequency rangesubstantially equal to said frequency intervals and including thefrequency of the lower sideband produced in said converter, meanscoupling said discriminator apparatus to said frequency converter, and acoupling between said frequency discriminator apparatus and saidfrequency control apparatus, said frequency control apparatus includinga reactance tube in the oscillation generator circuit and a motor fordriving a tunable element in said circuit, said reactance tube and. saidmotor being utilized to automatically tune said generator toapproximately the desired frequency as selected by the means used toselect the desired one of the plurality of fixed frequencies and by themeans used to tune the tunable discriminator.

HARRIS A. ROBINSON.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Name Date Re. 22,587 Varian et al. Jan. 2, 19452,404,852 Koch July 30, 1946 2,410,817 Ginzton et al Nov. 12, 19462,425,922 Crosby Aug. 19, 1947 2,521,070 Lindner Sept. 5, 1950

